The polyphenylene ether resin and the polyester resin components of the present invention are, in general, two thermodynamically immiscible polymers and compatibilizers are usually employed in blends of such resins.
For example, Yates III, U.S. Pat. No. 4,786,664 discloses blends of polyphenylene ether, with or without polystyrene resin, in combination with linear polyesters in a weight ratio of less than 1.2:1 in which a compatibilizer comprised of an aromatic polycarbonate can be used as a compatibilizer. The aromatic polycarbonate can be blended with a polystyrene resin. The compatibilizing agent can also be a polycarbonate-polyester copolymer, a polycarbonate polyester blend, or a polyphenylene ether-polycarbonate copolymer.
Similar compatibilizers for polyphenylene ether-polyester blends are described in Brown et al., U.S. Pat. No. 4,806,297; Yates III, U.S. Pat. No. 4,816,510; Brown, U.S. Pat. No. 4,831,087; Brown et al., U.S. Pat. No. 4,866,130; and Brown, U.S. Pat. No. 4,927,881.
In Sybert, U.S. Pat. No. 4,845,160, there are disclosed polyphenylene ether-polyester blends which are compatibilized by the use of polyphenylene ether/polyester copolymers.
In Bopp et al., U.S. Pat. No. 4,879,346, there are described blends of silicone-polycarbonate block copolymers with a compatibilized alloy of polyphenylene ether resin/polyester resin in which the polyphenylene ether resin and polyester resin are compatibilized through the use of aromatic polycarbonates or rubber-modified impact modifiers.
In Brown et al., U.S. Pat. No. 4,902,753, there are disclosed polyphenylene ether-polyester compositions which are compatibilized with the combination of a polycarbonate bisphenol-A homopolymer and a polycarbonate-polyphenylene ether-polycarbonate block copolymer.
In European published Patent Application No. 0 338 269, there are disclosed compatibilized polyphenylene ether-polyester compositions which are free of polycarbonates, and which comprise less than 800 ppm of nitrogen in the polyphenylene ether, and which are compatibilized through the use of specific polyesters in the claimed compositions, which polyesters are said to eliminate the need for polycarbonates therein.
It has now been discovered that a blend of polyphenylene ether resin and polyester resin can be effectively compatibilized through the use of a copolymer comprised of one or more polycarbonate resins and one or more polystyrene resins. In contrast to the compatibilization of polyphenylene ether-polyester blends of the above-mentioned prior art, the compatibilization effected by the copolymers of the presently claimed invention is independent of the weight ratio of polyphenylene ether to polyester in the blends and is independent of the nitrogen content of the polyphenylene ether utilized in the blends. Preferably, in the present copolymer compatibilizer, the polycarbonate resin is a bisphenol-A resin and the polystyrene resin is homopolystyrene. The compositions of the present invention exhibit superior impact strength and other physical properties, especially as compared to compositions comprising equal amounts of polycarbonates and polystyrene resins as are present in the presently claimed copolymers.